Originally Posted by
johns7022
Lord, I think you bring up some good points...but at the end of all this...your either a thinking pilot or a robot....if you assume that all planes fly after V1, it's just hoping, upon prayers, upon assumptions, made by engineers years and years ago..that what ever happened to your plane prior to rotation will not be something that has taken out your flight controls, created a structural failure ect.
I have been patient while restricting counter arguments to dumb scenarios where the assumption is that all flights seem to work in a world where balance field calculations always seem to run up to the end of an over run, with a cliff at the end, a lava pit at the bottom. If people can't convince me that all brakes fail while performing an RTO 1 kt past V1, they are convinced that all the runways in the world magically roll up the pavement to match balanced field calculations for that day...all the while building a lake full of Great White Sharks at the end...in some silly effort to make us believe that an RTO that stops the plane 1 foot after the balanced field calculations will result, 100% of the time with a plane careening to the scene of a horrible accident.
Correct - not all runways are such that you are truly operating with ASDR=ASDA. But unless you actually do the calcs - which for a line pilot, or even an airline performance department, involves going OUTSIDE the scope of the approved data - you have no idea what actual margin you have.
Correct, not all runways have a hostile overrun area. But many do, and even a benign overrun area can cause all kinds of damage if entered at speed. Airliner undercarraiges are not designed to be offroad capable.
Correct, not all brakes fail if used from 1kt above V1. But if V1, today, happens to be set by V1mbe, NO-ONE at any OEM will guarantee that the brakes will not fail. Sure, not every chamber in the revolver has a bullet in it. How many chambers make Russian Roulette a "safe and rewarding game"?
If I look at what we do when we actually conduct the max KE brake demonstration, we have "minimum crew" - because we want to limit the number of deaths we risk. We have those crew wear fireproof suits and the like - in the hope that they might have time thereby to escape the aflame vehicle. We have airport CFR actually present, at the predicted stop point of the test, so that if it all goes pear shaped they
might get the the aircraft before its engulfed in flames, and thereby rescue the test crew. And we inspect the hell out of the aircraft - especially the wheels and brakes assemblies - so that we understand exactly what kinds of risks we are running.
When you take your aircraft potentially
past max KE speed and then decide to brake, you have NONE of these mitigating factors. Sure, there are some conservatisms in the flight test demo - we use worn brakes, for example. But NOT 100% worn - how worn are YOURS? Our tyres are in decent shape - are yours? All it might take is one bad tyre, that lets go early. Suddenly now you have to do the rest of the stop on just three brakes, not four. You're going to be pushing all the remaining energy into those other three brakes - probably inducing more problems. As the brakes heat they are going to fade - not fail, 'just fade'. Which means they are going to stop working as well as you'd like. But of course you can't estimate what that might mean - because the OEM data asumed you'd not be pushing the brakes so hard. Faded brakes are going to take MUCH longer to bring you to a halt - we'll find out how much longer by measuring the distance to the written off airframe, in all likelihood.
I
will agree that there are some circumstances, where an aircraft will not fly, where aborting at Vr (if above V1) may be the only option. But you may well be at that point be picking - because you have no choice - a very bad second option only because the first option simply isn't available to you. I don't mind discussing the idea of what would happen for an abort outside the norms. But to pretend there is no significant risk in such an abort - that's just not helpful.